Recently, it has been required that the safety of a passenger, upon a collision, is improved. The mounting rate of various air bags has, thus, increased. An air bag is an inflatable cushion which is rapidly deployed and inflated, with gas flowing from an inflator into the inflatable cushion, when a sensor detects an impact upon a head-on collision or lateral collision of a vehicle, so that the impact applied to the passenger is mitigated to protect a human body due to the cushioning action of the inflated bag.
The air bag was initially applied to a driver's seat, then to an assistant's seat, particularly at a position on a front side thereof, mainly for the purpose of protecting a face and/or an upper half of the body of a passenger upon the head-on collision of the automobile. Recently, a curtain-shaped air bag has been developed, capable of coping with a lateral collision or a roll-over collision of the vehicle.
The curtain-shaped air bag is accommodated in an area from a front pillar side to a rear pillar side along a roof rail of a compartment side wall and is designed to inflate/deploy along a side window upon collision, wherein inflatable bag portions are formed at a plurality of positions. The curtain-shaped air bag is required to be excellent in containment ability (capable of being compactly folded) and it has a high inflation/deployment speed upon the collision since it must instantaneously appear between the passenger's head and a glass window to protect the head. Also, a required characteristic is that the internal pressure of the inflated air bag is not reduced in a short time but is maintained at a suitable level for several seconds after the deployment as a countermeasure against a roll-over collision. As the curtain-shaped air bag has a complicated configuration, it is often woven by a loom capable of weaving a high-density hollow weave fabric although it may be manufactured by a sewing operation. The air bag thus woven must be free from burst air-leakage problems upon inflation. The woven high-density double weave fabric consists of inflatable double layer portions and a single layer portion separating the double layer portions from each other. In the prior art, a boundary between the double layer portion and the single layer portion has often been problematic due to its weave structure in that fluffs appear on the high-density hollow weave fabric or the mechanical strength of the fabric is lowered by the generation of wrinkles.
When the curtain-shaped air bag is manufactured by a sewing operation, as in the prior art, a plurality of fabric sheets are prepared by cutting and are then sewn together. In this case, a sealant is sandwiched between the fabric sheets to be sewn together to prevent air from leaking through stitches as well as a thick sewing needle is used for the purpose of obtaining the anti-burst property. This, however, results in a problem in that the containment ability becomes worse. Also, as the configuration of the air bag is complicated, the sewing operation is troublesome.
Japanese Unexamined Patent Publication No. 1-254446 (Kokai) discloses that a bag-shaped high-density woven fabric wherein the outer periphery of a hollow weave portion is closed with a single-layer weave portion is used as an air bag. While it is necessary to use a single-layer weave portion larger in width to maintain the inflated state of the hollow weave portion, and there is a problem in that wrinkles or fluffs generate in a boundary between the hollow weave portion and the single-layer weave portion since a crimpability of a yarn in the single-layer weave portion is larger than that of a yarn in the hollow weave portion and also a cover factor of the fabric is larger, it is impossible to suppress air leakage for several seconds after inflation and deployment. Particularly, there is a problem in that wrinkles are liable to be generated due to heat or tension applied to the fabric when the surface of the fabric is coated with silicone resin or urethane resin to be suitable for the air bag.
Japanese Unexamined Patent Publications (Kokai) No. 3-16852 and No. 4-193646 propose a method wherein a seam zone is formed by encircling the outer periphery of a circular double-layer hollow weave portion with a single-layer weave portion consisting of two kinds of weave patterns to strengthen the seam zone. However, there is a problem in that, while the strength of the seamed portion itself is improved, it is still impossible to prevent air from leaking through the boundary between the double-layer hollow weave portion and the single-layer weave portion.
Japanese Unexamined Patent Publication (Kokai) No. 3-16850 proposes a method wherein the outer periphery of a circular double-layer hollow weave portion is encircled by two single-layer weave portions to form a seam zone and strengthen a seamed portion. However, there is no concrete description of a weave pattern of the single-layer weave portion therein and, as the width of the single-layer weave portion is too large, if such a fabric is used as a curtain-shaped air bag, there is a problem that warp yarns may be fluffy and the fabric may be wrinkled during coating.
Japanese Unexamined Patent Publication (Kohyo) No. 2003-510469 proposes a method wherein a plurality of single-layer portions of a basket weave pattern are formed around the outer periphery of a double-layer hollow weave portion to reduce the yarn shifting. However, this is problematic because the weave pattern in the single-layer portion is solely a 2/2 basket weave (throughout the specification, the term basket weave is used as the representing therm for basket weave including small-repeat basket weave such as hopsack weave, mat weave monk's weave and the like.) and the influence of a fineness of a yarn on the resulted fabric is not at all taken into account. As the 2/2 basket weave pattern has a tight structure and a load applied to a yarn is large, if a plurality of such weave patterns are adjacently arranged, there is a problem in that wrinkles are generated in a boundary between the double-layer hollow weave portion and the singe-layer weave portion to increase a bulkiness of the fabric, which deteriorates the containment ability. Also, the air leakage becomes high due to the irregularity of coating caused by the wrinkles.
Japanese Unexamined Patent Publication (Kokai) No. 2003-267176 proposes a method wherein a reversible hollow weave (reversible figured weave) portion is provided adjacent to a double-layer hollow weave portion to ensure air-tightness. However, there is no description in that a plurality of kinds of basket weave patterns are used for a single-layer weave portion arranged on the outer periphery of the reversible hollow weave portion. Accordingly, the air leakage is still unsatisfactory.
FIG. 7 is a schematic cross-sectional view of a conventional woven fabric of the above-mentioned type in the vicinity of a seam zone, and FIG. 8 illustrates a weave pattern of this fabric.
In the prior art, as shown in FIG. 7, two 2/2 basket weave portions are arranged in parallel with each other to form a seam zone. The 2/2 basket weave pattern has a tight structure and is effective for reducing the air leakage because the yarns cannot be shifted upon the deployment or inflation. However, in the high-density hollow weave fabric, if any such tight weave pattern like 2/2 basket weave is placed further outside thereof, wrinkles are generated in a bag portion interposed between the 2/2 basket weave portions or in the exterior of the 2/2 basket weave portion to cause irregular coating, resulting in air leakage.
As mentioned above, a high-density hollow weave fabric has not been obtained which is free from the generation of fluffs or wrinkles and solves the weavability and the air-leakage problems.